Bleaching composition



May 17, 1966 J. R. MOYER 3,251,780

BLEACHING COMPOSITION Filed May 11, 1964 Grams Nah C0 eer gram 600 Source INVENTOR- Job 0 R. Mayer United States Patent O Chemical Company, Midland, Mich., a corporation of Delaware Filed May 11, 1964, Ser. No. 366,367 3 Claims. (Cl. 252-186) This application is a continuation-in-part of US. patent application Serial No. 310,671, filed September 23, 1963, now abandoned.

This invention relates to a bleaching composition and, more particularly, to such a composition comprised of calcium peroxide and sodium bicarbonate and a process for using the same.

Aqueous hydrogen peroxide is extensively used as a bleaching agent in the bleaching industry. However, hazardous shipping and storage problems associated with the handling of aqueous hydrogen peroxide makes it desirable to provide instead a solid composition of matter which can be handled conveniently and shipped and stored safely without fear of decomposition, explosion and the like and which can easily be used in making aqueous hydrogen peroxide when this is so desired.

Sodium peroxide is a dry solid which can be used in making aqueous hydrogen peroxide. However, sodium peroxide as a solid thermally instable, losing a significant portion of its peroxygen value on prolonged storage through decomposition. It is also corrosive to personnel and to many materials thus making ordinary handling quite hazardous.

Calcium peroxide, on the other hand, in the usual commercial grades (75 percent CaO is a free flowing solid having a greater thermal stability than sodium peroxide in both short and prolonged storage and is noncorrosive to handling personnel and to the material it is likely to contact. It would thus be desirable to include calcium peroxide as the peroxygen source in a bleaching composition. Ordinarily, calcium peroxide is insoluable in water. However, this invention makes the peroxygen content of insoluble calcium peroxide soluble.

In a copending application, Serial No. 262,511, I have disclosed a bleaching composition prepared by admixing potassiumpyrosulfate with calcium peroxide in a weight ratio of pyrosulfate to peroxide within the range of from 3.4 to about 7.5 with sufficient water to make either a pasty aqueous composition, a slurry, or solution having a pH of from about 9.5 to about 1. A particular advantage of that bleaching composition is that the aqueous bleaching mixture prepared may have a pH of not greater than 3, if desired.

The bleaching composition of this invention may be added to water to produce an aqueous bleaching mixture which may have a pH ranging from about 12.13 to about- 9.60. This alkaline bleaching mixture is desirable over an acidic mixture in the bleaching of certain materials such as wood pulp. It may also be used in the bleaching of textiles.

Thus, it is an object of the present invention to provicle a free flowing solid composition of matter to be used for bleaching purposes employing calcium peroxide as the peroxygen source, which is stable upon prolonged storage, non-toxic in ordinary usage and substantially non-corrosive.

A further object of the invention is to provide a solid bleaching composition employing calcium peroxide so that when employed in' an aqueous mixture, a substantially complete release of its peroxygen value is obtained.

Another object is to provide a process for bleaching using a bleaching composition employing calcium per- .oxide as the peroxygen source.

An additional object is to provide a solid bleaching 3,251,786 Patented May 17, lgfifi composition and process for using the same wherein the mixture comprising the composition and used in the process, when in solution, is alkaline.

Other objects and advantages will become apparent from reading the detailed description disclosed hereinafter. a

In accordance with the invention, calcium peroxide is admixed with sodium bicarbonate in a weight ratio which ranges from about 1.5 to about 3.4 parts sodium bicarbonate to each part of calcium peroxide to form a bleaching composition such that when said composition is mixed with water, the solution is alkaline and within a pH range of from about 12.13 to about 9.60 and a complete release of the peroxygen value is obtained.

In one embodiment of this invention, a bleaching composition is prepared by admixing sodium bicarbonate with calcium peroxide in a weight ratio which ranges from about 1.8 to about 3.4 parts sodium bicarbonate to each part of calcium peroxide. The mixture so obtained, when mixed with various amounts of water (e.g., from 1 to 250 parts of water per part of dry mixture) provides a pH of from about 11.5 to about 9.60. The amount of Water used is not sharply critical but is generally dependent upon the nature of the material to be bleached.

pHs ranging from 12.13 to 11.5 may be'obtained using a weight ratio of sodium bicarbonate of calcium peroxide ranging from about 1.5 to about 1.8 parts sodium bicarbonate to each part calcium peroxide with various amounts of water, for example, from 1 to 250 parts of water per part of the dry mixture. The desired pH value in this range is more easily attained by the addition of small amounts of either a standard base, e.g., sodium hydroxide, or an acid, e.g., hydrochloric acid.

At a pH of 12.13 and below, a substantially complete release of the peroxygen value of the calcium peroxide is obtained. Above a pH of 12.13, however, there is a significant reduction in the peroxide release. The weight ratios required to obtain the desired pH'within the above range are determined by reference to the graph in the annexed drawing.

The graph shown in the drawing is a plot of the pHv values obtained in the aqueous mixtures of sodium bicarbonate and calcium peroxide in the weight ratios shown.

In obtaining the pH values plotted on the graph, aqueous slurries were prepared by adding 1 gram of percent pure calcium peroxide and an amount of sodium bicarbonate to calcium peroxide represented by the heavy points on the graph to milliliters of Water. The pH of each of the so-prepared aqueous mixtures was determined by a Leeds and Northrup pH indicator in combination with a Beckman glass electrode. The peroxygen value of each mixture was determined iodometrically using starch as an indicator. In the mixtures whichregistered a pH below 12.13, a complete release of the peroxygen value of the calcium peroxide was noted. However, in the mixtures having a pH above 12.13, the release of the peroxygen value was reduced as the pH increased.

A particular advantage of the present bleaching composition is that the aqueous bleaching mixture prepared may have a pH of not lower than 9.60, if desired. Thus, materials such as wood and wood pulp can be elfectively bleached with such an alkaline solution.

In carrying out the method of this. invention, an aqueous mixture of sodium bicarbonate and calcium peroxide in a weight ratio Within the range stated above is prepared. The mixture is dissolved in that quantity of water needed to provide the desired pH applicable to the material being bleached. The material to be bleached is then contacted with said aqueous mixture for a time sufiicient to obtain the desired degree of bleaching, followed by removal of the so-bleached material from the aqueous mixture and rinsing.

The sodium bicarbonate ingredient of the bleaching composition of this invention provides the acid needed to form hydrogen peroxide, the actual bleaching agent, from the calcium peroxide according to the following reaction:

If other grades of pure calcium peroxide are employed in the bleaching composition of the present invention, the weight ratios of sodium bicarbonate to calcium peroxide as used in obtaining the points on the aforementioned graph will be substantially the same as those using commercially pure materials and will require only slight modificatiomas determined by testing, to produce the pH in solution as indicated in the graph.

To further illustrate the utility of the present invention as applied to bleaching wood pulp, aqueous bleaching mixtures were prepared in accordance with the instant invention, each having the composition and pH as indicated in Table I;

A batch of redwood kraft pulp was prebleached with 8 percent C1 4 percent NaOH and 2 percent NaOCl and was found to have a brightness after these three stages of 74.8 air dry and 70.5 oven dry (one hour at 105 F.). The so-treated pulp was immersed in each of the so-prepared aqueous mixtures, maintained at a temperature of about 160 F. for 180 minutes and air dried or oven dried at 105 F. for one hour. Magnesium sulfate and sodium silicate were added to the solution as a stabilizer to prevent peroxide decomposition. This is a conventional step in the wood pulp bleaching art. The brightness of each of the so-bleached batches was next determined by using a Photovolt Refiectometer with a Hunter green tristimulus filter, with MgO as a standard with a percent brightness of 100. The results of these tests are recorded in Table I.

In addition, as blanks for comparison purposes, two aqueous sodium peroxide solutions, a well known bleach for wood pulp, were prepared equivalent or greater in released peroxygen value to the above aqueous mixtures prepared under the same invention. Pieces of pulp of the same grade and type as above were also bleached using the same procedure and under the same conditions. The so-bleached pulp was tested for brightness with the results also recorded in Table I.

TABLE I The results shown in Table I clearly illustrate the utility and effectiveness of the composition of the present invention as a bleachant.

Various modifications can be made in the present invention without departing from the spirit or scope thereof, for it is understood that I limit myself only as defined in the appended claims.

What is claimed is:

1. A'dry thermally stable bleaching composition consisting essentially of sodium bicarbonate and calcium peroxide as a powdered mixture wherein the ratio of the weight of said sodium bicarbonate to calcium peroxide is from about 1.5 to about 3.4 such that when mixed together in quantities of water of from 1 to about 250 parts of water per part of dry mixture, an aqueous bleaching mixture is produced having a pH value within the range of from about 12.13 to about 9.60.

2. A dry thermally stable bleaching composition consisting essentially of sodium bicarbonate and calcium peroxide as a powdered mixture wherein the ratio of the weight of said sodium bicarbonate to calcium peroxide is from about 1.8 to about 3.4 such that when mixed together in quantities of water of from 1 to about 250 parts of water per part of dry mixture, an aqueous bleaching mixture is produced having a pH value within the range of from about 11.5 to about 9.60.

3. A dry thermally stable bleaching composition consisting essentially of sodium bicarbonate and calcium peroxide as a powdered mixture wherein the ratio of the weight ofsaid sodium bicarbonate to that of said calcium peroxide is within the range of from about 1.5 to about 1.8 such that when mixed together in quantities of water of from 1 to about 250 parts of water per part of dry mixture, an aqueous bleaching mixture is produced having a pH value within the range of from about 12.13 to about References Cited by the Examiner UNITED STATES PATENTS 2,366,740 1/1945 McEwen 8-1l1 JULIUS GREENWALD, Primary Examiner.

M. WEINBLATT, Assistant Examiner.

A comparison of the efiects of a solution of CaO and NaI-ICO with a solution of Na O in bleaching redwood kraft pulp Brightness 2 Percent Percent 41 Tcmper- (Percent) Example Source of Active Active B. Sodium Percent Final ature Oxygen Oxygen 1 Silicate 1 MgSO; 1 pH F.)

Air Oven Dry Dry NaHOOH-CaO; 0.205 2.0 0.025 11. 4 82.0 79. 2 NaHCOH-OaO 3 0.205 1.0 0.025 11.6 160 82.0 80.2 NagOz 0. 205 2. 0 0.025 10. 2 84. 2 82. 5 0. 2 1. 0 0. 025 10. 2 190 83. 2 81. 5

1 As weight percent of dry pulp. 2 Of dry pulp after bleaching. 9 One gram CaO to 1.75 grams NaHCOs/lOO ml. H O, 

1. A DRY THERMALLY STABLE BLEACHING COMPOSITION CONSISTING ESSENTIALLY OF SODIUM BICARBONATE AND CALCIUM PEROXIDE AS A POWDERED MIXTURE WHEREIN THE RATIO OF THE WEIGHT OF SAID SODIUM BICARBONATE TO CALCIUM PEROXIDE IS FROM ABOUT 1.5 TO ABOUT 3.4 SUCH THAT WHEN MIXED TOGETHER IN QUANTITIES OF WATER OF FROM 1 TO ABOUT 250 PARTS OF WATER PER PART OF DRY MIXTURE, AN AQUEOUS BLEACHING 